atc250r problem

[250rJAMIE]

Hi,
I've recently put my 83 250r back together a few weeks ago and there seems to be a big problem somewhere that I cant quite figure out. its been acting like this for about 6 months but its got really bad now.When I start it cold It idles heaps high then when it warms up it idles a little lower then when it gets a little hotter it does not idle/no back pressure as soon as I let of the throttle it just slows down and dies then takes about 7-10 kicks to get going again but if I let it cool down it starts right up within 2 kicks.I've replaced all top end gaskets,new carby and played around with the jetting for hours and hours at the dunes,new reeds.Its not burning oil and I replaced the stator side crank seal but it still does it.
I've recently replaced the bottom end bearings about a month ago but theres still a bit of play if I grab the crank and move it up and down.Now I think thats not normal and The crank is a little flogged out...could this be the problem? am I up for another crank cause I have no idea what else it could be


Thanks

[dcreel]

Have you checked the compression? It also sounds like you may have an intake side air leak. The temperature changes may be affecting the size of the air leak.

[BOB MARLIN]

Try to richen up on the jets and change the needle position. A lean carb will cause the idle to go up and down and you won't be able to adjust it out with the adjustment screws.

[250rJAMIE]

I've played around with the jetting all weekend at the dunes (different needles/pilots) and it still done it.I swapped to a different carby and another carby boot again with new reed gaskets and gasket sealant on them and also another stator side crank seal but its still doing it..
I have to chase down a compression tester so I can see what the top end is like but the rings in it are not that old either.
Any other ideas??
Thanks

[Grizzlypeg]

On a 2 stroke engine, the crankcase is effectively part of the intake system. Vacuum leaks there are just like leaks in the intake manifold and cause lean mixtures. I've only had a few 2 stroke bikes, but none had play in the crankshaft like you describe. You might be describing the source of your problem. Watch out, because 2 strokes can be easily damaged by lean mixtures.

[jeffatc250r]

My vote is an air leak. Quite likely the crank seal on the ignition side.

[fabiodriven]

My vote is an air leak. Quite likely the crank seal on the ignition side.

Ding! Ding! Ding!

If you have play in the crank I can almost guarantee that's your problem.

[250rJAMIE]

thanks for the replys...I say its the crank.I replaced the bearings about a month ago and theres still play in it..Anyways I got the motor out of it and ripped apart.I got the crank out and I sat a a new crank seal on it then sprayed a little WD around it and waited a few minutes and it was slowly leaking through...now that shouldnt do that??
Got to wait til pay day next week and start looking for a decent crank that dont need rebuilding.
Thanks

[250rJAMIE]

Ok update....the piece if trailprotrailprotrailprotrailpro is still playing up..new bottom end bearings,new bottom end seals,another complete crank,All new gaskets and its still playing up.I checked and checked all the cases and everything looks fine the piston/rings,cylinder look all fine, new rings about 7months ago with about 40 hours on them so far.It starts up fine but smokes holly hell and as soon as it warms up it looses all back pressure and doesnt want to idle then if I turn the idle all the way up it goes ok but still not 100% but as soon as I let it cool down for about 15mins or so it idles way way high when I start it back up then have to back the idle screw all the way out.I got the motor apart again at the moment and the piston was covered in gunky unburnt oil and a huge puddle of fuel down the bottom of the crank case.It doesnt seem to be burning gearbox oil.Im running 32:1 with a br8es plug...could it need a hotter plug for it to burn the oil or change to a better 2 stroke oil.or could it be electrical like the coil not sparking right when it gets to a certain running temperature?? any help will be appreciated..I really want to get this thing running right so I can finally have a decent ride on it.
Thankyou

http://i134.photobucket.com/albums/q87/blaster_021/DSC01715.jpg